Swine influenza was first recognized in pigs following the emergence of the 1918 “Spanish Flu” pandemic, and was first isolated in 1930 by Richard Shope (Jour Exp Med 54:373-385 (1931)). This “classical” swine virus (cH1N1) continued to circulate and evolve in pigs until the mid-1990s when a triple reassortant (tr) between a North American avian, a human H3N2, and the cH1N1 was identified (Zhou et al. Jour of Vir 73:8851-8856 (1999)). This new trH3N2 virus quickly reassorted again with the cH1N1's to produce a wide range of subtype constellations (H3N2, H1N1, H1N2, etc.), all with the same triple reassortant, internal gene cassette (TRIG) composed of avian-origin PB2 and PA genes, human-origin PB1, and swine-origin NP, M, and NS genes. The diversity of this virus pool has since been increased with the introduction and establishment of human-origin H1N1 and H1N2 viruses containing the TRIG cassette in US swine populations (Vincent et al. Adv in Virus Res. 72:127-154 (2008)).
The virulence of these viruses varies widely, but infection may result in fever, anorexia, and abortion in pregnant sows resulting in an overall decline in pork production for affected farms. A number of methods have been employed, however, to control this burden. Vaccination and biosecurity have become the most common method to prevent the spread of influenza and to ease the disease burden on the population. Today, inactivated influenza vaccines are commonly available and are designed to match the most common circulating strains. Nevertheless, while these commercial vaccines are available, limited protection is observed in practice due to the antigenic and genetic diversity of influenza viruses circulating in pig population. Furthermore, continued use of these commercial vaccines will most likely result in immune pressure and antigenic divergence of circulating viruses necessitating the reformulation of commercial vaccines. For these reasons, many swine producers have turned to autogenous vaccines to better match strains circulating within their own herds. The use of autogenous influenza vaccines have grown rapidly in recent years due to the diversity of viruses circulating in US pig populations (Vincent et al. Adv in Virus Res. 72:127-154 (2008)). While they are not yet approved for use in swine, live-attenuated influenza vaccines (LAIV) have been shown to provide significant protection to homo- and heterosubtypic challenge in both human and swine models (Loving et al. Journ of Virol 87:9895-9903 (2013)). While both autogenous and LAW could fill an efficacy void left by commercial vaccines, their production still relies heavily on virus growth in eggs or tissue culture systems.
A major drawback in the preparation of LAW and KV vaccines is that production relies on a heavily time-consuming process of growing the viruses in eggs or tissue culture cells. Additionally, since most influenza strains grow poorly in these systems, vaccine strains are produced from reassortants that generally carry the surface gene segments from the candidate virus and other segments from a high growth donor virus. Reverse genetics (RG) has improved the ability to generate such high growth reassortants; however, growing influenza viruses in eggs or tissue culture may result in adaptive changes on the viral surface proteins resulting in antigenic mismatch. LAIV vaccines have an advantage over KV vaccines since they produce broader responses by stimulating both the humoral and the T-cell arms of the immune system. The 2009 pandemic H1N1 virus (pH1N1), however, highlighted the fact that these traditional vaccine production systems are too slow to significantly ameliorate or alter the impact of a pandemic given that the initial pH1N1 vaccine candidates were not well suited for growth in eggs. Alternatively, egg-free influenza vaccine strategies have been investigated including recombinant viral proteins, recombinant viruses, and virus-like particles (VLPs). FLUBLOK™, a baculovirus-based recombinant hemagglutinin influenza vaccine, is the only influenza vaccine approved for human use that does not rely on traditional production systems, but it must also undergo reformulation as a result of antigenic drift. No such vaccines are available for swine.
Type A Influenza (Flu) viruses, also known as influenza A viruses (IAVs), belong to the family Orthomyxoviridae and their genome consists of eight segments of single-stranded RNA of negative polarity (Webby R J, et al. (2007) Cur.r Top. Microbiol. Immunol. 315: 67-83; Yamanaka K, et al. (1991) Proc Natl Acad Sci USA 88:5369-5373; Lopez-Turiso J A, et al. (1990) Virus Res 16: 325-337). The virus has an envelope with a host-derived lipid bilayer and covered with about 500 projecting glycoprotein spikes with hemagglutinating and neuraminidase activities. These activities correspond to the two major surface viral glycoproteins: the hemagglutinin (HA) and neuraminidase (NA), present as homotrimers and homotetramers, respectively. Within the envelope, a matrix protein (M1) and a nucleocapsid (NP) protein protect the viral RNA (Lamb, 1989). The type designation (A, B, or C) is based upon the antigenic features of the M1 and NP proteins. Approximately half of the total genome encodes for the three viral polymerase proteins (segments 1,2 and 3; (Palese et al., 1977). Segment 5 encodes the NP protein. The three-polymerase subunits (PB1, PB2, and PA), the NP and the vRNA are associated in virions and infected cells in the form of viral ribonucleoprotein particles (vRNPs). Segments 4 and 6 encode for the HA and NA genes, respectively. The two smallest segments (7 and 8) encode two genes each with overlapping reading frames, which are generated by splicing of the co-linear mRNA molecules (Lamb and Lai, 1980; Lamb and Lai, 1984; Lamb et al., 1981). In addition to M1, segment 7 encodes for the proton pump transmembrane protein (M2), which has ion channel activity and is embedded in the viral envelope. Segment 8 encodes for NS1, a nonstructural protein that blocks the host's antiviral response, and the nuclear export protein (NS2 or NEP) a structural component of the viral particle. NEP/NS2 interacts with the cellular export machinery and participates in the assembly of virus particles. Recently, NEP/NS2 has also been implicated in playing a role in the regulation of influenza virus transcription and replication. Thus, the eight RNA segments encode for 10-12 viral proteins, including two surface glycoproteins, HA and NA, M2, M1, NS2/NEP, NS1 and, in some influenza viruses (from an alternative translation start site in segment 1) the PB1-F2, an apoptosis modulatory protein [Arias C F, et al. (2009) Arch Med Res 40: 643-654; Zell R, (2006) Emerg Infect Dis 12: 1607-1608; author reply 1608-1609; Chen W, et al. (2001) Nat Med 7:1306-1312.]. Additional viral protein products include PB1-N40, derived from an alternative start site within the PB1 ORF, resulting in a protein product that lacks the first 39 aa of PB1, and PA-X, derived from the PA mRNA and consists of the N-terminal 191 aa of PA fused to 61 aa that result from +1 frameshifting [Jagger B W, et al. (2012) Science 337: 199-204; Yewdell J W, Ince W L (2012) Science 337: 164-165.].
What is needed are methods and compositions for stimulating the immune system of an animal, such as by vaccine methods, wherein the antigenic composition or vaccine, does not need to be manufactured in tissue culture conditions, but instead, the vaccine composition is produced in the subject's body directly. What is needed are compositions and methods of treatment for reduction of infection by vaccination comprising vectors comprising polynucleotides that express pathogenic or oncogenic antigens that stimulate the immune system of a subject to whom the vector is provided. In particular, what is needed are methods and compositions for stimulating the immune system of a pig such that a vaccine composition can be manufactured directly in the pig's body directly.